Removal of phenols from hydrocarbons



REMOVAL OF. PHENOLS FROM HYDROCARBONS Filed Feb. 12, 1931 w 0 N Ma a FA w EM M wF W MA CONTAINING WATER FORMIC ACID VAPORS DISTILLED OFF MIXTURE OF PHENOLS AND FORMIC AC ll] CONTAINING WATER cm cowuzrqsso fioRmc ACID FOR'MIC [CONDENSED FORMIC ACID MIXTURE OF PHENOLS AND FORMIC ACID CONTAINING WATER FmiZ scizwamle Patented Nov. 7, 1933' UNITED STATES PATENT OFFICE REMOVAL OF PHENOLSV FROM- HYDROCARBONS Hans Boos and Schwamberger, Ludwigshafen-on-the-Rhine,- Germany,

Farbenindustrie assignors to Aktiengesellschaft,

Frankfort-on-the-Main, Germany Application February 12,1931, Serial No; 515,254, and in Germany February 20, 1930 17 Claims.

'the widespread but very expensive alkali process. The said extraction processes are attended by the objection that the solvents employed have no specific solvent power for the phenols; either considerable amounts of neutral oil are also extracted or else only an incomplete removal of phenols is effected. V

It is already known that formic acid, especially anhydrous formic acid, is a solvent for phenols, whereas the hydrocarbons are practically not absorbed thereby. No use has hitherto been made of the industrial application of this fact because it was thought that when the formic acid containing phenols is distilled a part of the acid would be retained by the phenols by the formation of esters. Moreover it was assumed that when employing formic'acid in circulation with oils containing water a considerable dilution of the formic acid would take place so that after a short time it would lose its property of being a solvent for phenols.

We have now found contrary to expectation that the mixture of phenols and. formic acid obtained by employing formic acid as the extracting agent in the recovery of phenols from tar oils or other hydrocarbon mixtures containing phenols can be separated completely by distillation without the formation of esters. When working in this manner, the formic acid may be employed again since even when employing oils containing large amounts of water the objectionable dilution of the formic acid is not noticeable because by the distillation any absorbed water is readily separated from the formic acid.

The separation of the mixtures of formic acid and phenols by distillation is very simple because the boiling point of formic acid is slightly above 100 C. while that of the phenol of lowest boiling point is about 180 C. In consequence of the property of formic acid in admixture with water of giving a boiling point maximum at 107.1 C. when the strength is 77.5 percent, it is readily possible to employ the formic acid again in circulation, and more dilute formic acid solutions may always be concentrated to 77.5 percent strength by appropriate distillation. This concentration is quite suificientfor the removal of the phenols. It is therefore quite simple in the results.

treatment of hydrocarbons-containing water to adiust them from the start to this acid. In the extraction of oils free from water .it is obviously advantageous to employ an acid having a higher content, as for example up to 100 percent. The concentration of formic acid most advantageously employed also depends on the nature of the oils treated. Thus when treating oils rich in phenols such as pit coal tar oil it is often more advantageous to employ rather dilute acids, and

even formic acid of percent strength is very suitable. On the other hand when treating oils poor in phenols, such as brown coal tar oils more concentrated solutions of formic acid give better The invention is, however, not limited to operations carried out with the concentrations of formic acid specified.

A further very important advantage of the process according to the present invention consists in the fact that the phenols obtained are quite pure. They dissolve completely in alkali so that neutral oils are not simultaneously dissolved out,

A further advantage is the fact that the high specific gravity of the formic acid effects aready separation of the neutral oil from. the formic acid containing phenols. 1 It should be emphasized that this separation takes place immediately without any formation of an emulsion.

When working up very viscous tars and oils it is more advantageous to extract them-at elevated temperatures. Pressure may then be employed to avoid any loss of formic acid.

In practice, the process according to the present invention may be carried out for example as follows:

The oil from which it is desired to remove the phenols is shaken or stirred with formic acid for some time at room temperature or at an elevated temperature which lies'above the setting point of the oil or tar. After satisfactory mixing the shaking or stirring is discontinued and the separation into two layers takes place imme diately without the formation of an emulsion. The formic acid containing phenols is withdrawn, the acid and the phenols separated from each other by distillation and the former continually supplied to the oil again until the phenols have been completely removed. No loss of formic acid occurs since practically the whole of the formic acid is recovered by distillation. The amount of formic acid employed depends on the amount of phenols present in the oil. As a rule four parts by weight of formic acid are employed for each part by weight 'of phenol.

As initial materials may be mentioned liquid hydrocarbons from any source containing phenols, as for example brown coal tar, brown coal tar distillates, mineral coal tar, wood tar, low temperature tar, destructive hydrogenation products of coals, tars, oils and the like containing phenols.

When working in the before described manner it sometimes occurs that small amounts of formic acid are retained in the neutral oil, especially when employing oils and tars containing constituents of aromatic nature and/or those of high boiling point, for example of more than 300 C. Attempts to recover this formic acid by washing with water do not have the desired result by reason of the large amounts of water necessary. Likewise recovery by way of solid formates is not successful.

The retained formic acid may be recovered in a simple manner by distilling off the fraction of low boiling point, such as a fraction boiling up to at least 110 C., as'for example the fraction passing over between about -100 and 130 C., of

the hydrocarbons freed from phenols. The dis tillate then consists of two layers, the lower being pure formic acid which may be readily separated from the upper layer of neutral oil.

When working up oils containing water the phenols retain the water in the mixture to be extracted so firmly that it is not given up to the formic acid during the extraction but only .dur-

ing the separation of the formic acid from the phenol mixture by distillation. The water is then split off and it dilutes the formic acid which distils over. As stated in the foregoing it is often desirable to operate with formic acid of high concentration.

We have found that the dilution of the formic acid with water is avoided by distilling the formic acid off at temperatures below 100 C. under reduced pressure. The formic acid then passes over in a concentrated form and thus does not require rectification, whereas at atmospheric pressure only a 77.5 per cent acid is obtained. When distilling the mixture of formic acid and phenols, under the said conditions, the phenols retain the water, and it may be removed to a great extent by heating said phenols at ordinary pressure to the boiling point of water.

In many cases it is preferable only to distil off the greater part of the formic acid under reduced pressure, the remainder being distilled off together with the water at. atmospheric pressure. A small fraction of fairly dilute formic acid is thus obtained. This acid may be concentrated by distillation at atmospheric pressure, and when a concentration of more than 77.5 per cent is required, by'distillation under reduced pressure, advantageously in admixture with concentrated sulphuric acid. The amount of sulphuric acid depends on the dilution of the formic acid .to be concentrated and on the desired final concentration of the latter. It is not necessary to distil the formic acid in a very high vacuum, that is at very low temperatures,

because the formic acid always contains traces of oils and resins which retard the decomposition of the formic acid which would otherwise readily occur. Usually pressures ranging from 15 to 40 millimetres mercury gauge are employed. The distilled formic acid is free from resinous substances. Distillation under reduced pressure is therefore very advantageous for the treatment also of oils free from water; and in particular for the treatment of oils containing resins or substances having a tendency to resinify.

The concentration and purification by means of sulphuric acid is also preferable with slightly dilute formic acid. For the continuous recovery of formic acid from its mixture with phenols by distillation in vacuo it has proved advantageous to effect this distillation in morethan one distilling vessel. In this manner an acid of constant concentration' may be obtained. The accompanying drawing shows diagrammatically an arrangement for carrying out this modification of the process but the invention is not restricted thereto. The mixture of phenols and formic acid obtained by the extraction with a formic acid of a concentration of say per cent is collected in the vessel 3. From thence it is supplied to the distilling vessels 1 and 2. The vapors issuing from the said vessels 1 and 2 are united in a condenser 4. Thedistillation is initiated in only one of the distilling vessels for example in the vessel 1, and at first an acid of a content of about 87 per cent will be carried over to the condenser 4. The concentration of distilled acid then gradually falls 'and when it is less than 85 per cent the mixture contained in the vessel 2 is brought to distillation similarly furnishing at first an acid of high concentration, so that the combined vapors issuing from the vessels 1 and 2 will have an average concentration of 85 per cent. This is continued until the acid contained in the vessel 1 is completely distilled off. At this moment also the vapors issuing from the vessel 2 will have a reduced concentration, so that it is necessary to distil a fresh mixture of phenols andformic acid supplied from the vessel 3 to the vessel -1 and so on.

The process may also be carried out continuously by passing the oil to be dephenolized up wards through a column filled with Raschig rings, sieves, or similar devices, while formic acid is allowed to fiow downwards in counter-current. When employing a formic acid having an initial concentration of less than 77.5 per cent the acid is distilled on from the mixture thereof with phenols at ordinary pressure with the employment of rectifying columns and after being brought to its initial concentration, it is returned to the process. When employing an acid of a concentration of morethan 77.5 per cent it is preferable to effect the separation of the phenols and the formic acid under reduced pressure. The extraction with formic acid may also be carried out in several stages, the concentrations of the formic acid being varied (preferably increased), if desired. After the second extraction the separation of the acid from the phenols may be carried out under ordinary pressure even when employing an acid of a concentration of more than 77 per cent. It has been found that the phenols containing appreciable amounts of ,water are removed already by the first extraction. The formic acid therefore may be recovered in its original concentration by distillation under ordinary pressure from its mixture with phenols obtained by the second extraction, even if the oil treated in the first extraction contained appreciable amounts of water. It has also been found that when working according to the present invention it is not even necessary to remove the pyridine bases from tars and tar oils prior to the extraction of the phenols as was hitherto usuallyeffected. No losses of formic acid on account of formation of formates of pyridine occurs but the whole amount of the formic acid may be recovered by distillation of the mixture of phenols and formic acid even if pyridine bases are present. The pyridine and the phenols form a compound which isapparent- 1y very stable. No formate of pyridine which boils at about 145 C. distils over. The pyridine is completely contained in the phenols separated from the formic acid and may be recovered therefrom, for example by treatment with mineral acids.

The phenols containing pyridine, in particular those obtained from mineral coal tar middle oil, so-callecl carbolic, may be employed for chemical conversions of different kinds as for example for the production of phenol phosphates or phenol carbonates. With particular advantage they may be used for the direct production of resinous masses having excellent properties, for example by condensation in the usual manner with formaldehyde or similar aldehydes, the pyridines present in the phenols acting as a catalyst. In the usual subsequent distillation of the water from the condensation products the pyridine bases distil over and may then be readily recovered from the distillate.

The following examples will further illustrate the nature of this invention, but the invention is not restricted to these examples- The parts are by weight.

Example 1 100 parts of a brown coal mobile tar are treated for several hours at ordinary temperature with 5 parts of 77.5 per cent formic acid in any continually acting liquid extraction apparatus of known design. After separating the layer containing the formic acid and distilling.

off the acid 10 parts of a creosote completely soluble in alkali are obtained. The mobile tar which is considerably paler in'color is practically free from phenols. 1

Example 2 Example 3 100 parts by volume of a crude benzine having a phenol content of 1.3 per cent obtained by the destructive hydrogenation of brown coal low temperature tar are treated withthe same volume or ten times with 10 parts by volume each time of 77.5 per cent formic acid. The benzine, which is considerably improved in odor and color, has a phenol content of 0.1 per cent.

The formic acid is distilled off. As first runnings 10 parts of an about 68 per cent acid and then 10 parts of an about 72 per cent acid are thus obtained. The main fraction consists of parts of a 77.5 per cent formic acid which is instantly returned to the process. The first runnings, if desired, together with .the first runnmgs obtained in preceding operations are then concentrated by repeated distillation to a 77.5 per cent acid.

Example 4 100 parts of a mineral coal tar fraction boiling between 150 and 220 C. and containing 40.7 per cent of phenols are treated 5 times with 10 parts of a 77.6 per cent formic acid. The remaining oil contains only 1.2 per cent of phenols. 38 parts of a mixture of phenols which completely dissolves in an alkaline solution may be obtained from the formic acid. The regeneration of the formic acid may be effected as described in Example 3.

Example 5 100 parts of a brown coal low temperature carbonization tar containing about 20 per cent of phenols is treated with'lO parts ofa 77.5 per cent formic acid as described in Example 1. 19 parts of phenols soluble in alkaline solution are obtained from the formic acid. The content of phenols of the remaining tar is lessthan-l per cent.

Example 6 100 parts of a wood tar fraction boiling up to 210 C. and containing 25 per cent of phenols is extracted 5 times with 10 parts of a 77.5 per cent formic acid. 24 parts of phenols soluble in alkaline solution are obtained fromthe formic acid. The remaining oil contains only 0.5 per cent of phenol.

Example 7 100 parts of a peat tar fraction containing 40 per cent of phenols is treated 10 times with each 10 parts of 77.5 per cent formic acid. 39 parts of phenols are obtained from the formic acid.

The resulting oil contains only 0.6 per cent of phenols. The formicacid is regenerated as described in Example 3.

Example 8 Example 9 100 parts of a brown coal, tar boiling from 200 to 300 C. and having a creosote content of 25 1 per cent are treated with 100 parts of 83 per cent formic acid. When working continuously,

this treatment is preferably carried out by leading the tar oil upwards through a vertical tube filled with Raschig rings, the formic acid being allowed to flow downwards in counter-current. By distilling the mixture of formic acid and phenols leaving atthe bottom in vacuo, 95 parts of 83 per cent formic acid are obtained while 5 parts of 82.5 per cent formic acid are obtained by distilling the neutral oil. The phenol content of the neutral oil amounts only to 0.5 per cent.

When the mixture of formic acid and phenols is distilled at atmospheric pressure, 99 parts of 78.7 per cent formic acid are obtained which continually become more dilute when employed again.

Example 1 0 .cent formic acid in the usual manner by adding 0.5 part of concentrated sulphuric acid and distilling in vacuo.

Example 11 100 parts of a mineral coal tar-middle oil boiling between 150 and 200 C. and containing 25 per cent of phenols and 5 per cent of pyridine bases is treated as described in Example 1 with 100 parts of 77.5 per cent formic acid. 70 parts of neutral oil which is almost free from phenols and pyridines, are obtained. After distillation of the 100 parts of formic acid from the layer containing the formic acid 30 parts of phenols containing pyridines are obtained which may be worked up in the usual manner to condensation products having excellent properties.

What we claim is:--

1. A process for dephenolizing a liquid hydrocarbon containing aphenol, which comprises treating said liquid hydrocarbon with formic mic acid, separating the mixture of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling the formic acid from said mixture, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon. 7

2. A process for dephenolizing a liquid hydrocarbon mixture containing constituents of high boiling point and containing phenols, which comprises treating said hydrocarbon mixture with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from the liquid hydrocarbons, removing any formic acid retained in the hydrocarbons by distilling therefrom a fraction of low boiling point, separating the formic acid from said fraction of low boiling point, distilling the formic acid from the mixture thereof with phenol, and employing the distilled formic acid again for dissolving phenols' contained in a liquid hydrocarbon mixture.

3. A process for dephenolizing a liquid hydrocarbon mixture containingconstituents of arcmatic nature and containing phenols, which comprises treating said hydrocarbon mixture with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from the liquid hydrocarbons, removing any formic acid retained in the hydrocarbons by distilling therecontained in a liquid hydrocarbon mixture.

4. A process for dephenolizing a liquid hydrocarbon mixture containing constituents of high boiling point and those-of aromatic nature and containing phenols, which comprises treating said hydrocarbon mixture with formic acid,

formic acid thus obtained from the liquid hydrocarbons, removing any formic acid retained in the hydrocarbons by distilling therefrom a fraction of low boiling point, separating the formic acid from said fraction of low boiling point, distilling the formic acid from the mixture thereof with phenol, and employing the distilled formic acid again for dissolving phenols contained in a liquid hydrocarbon mixture.

5. A process for dephenolizing a liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling under reduced pressure the formic acid from said mixture, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

6. A- process for dephenolizing a liquid'hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol andformic acid from said liquid hydrocarbon, dis tilling the formic acid from said mixture, under such reduced, pressure that the distillation occurs below 100 C., and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

7. A process for dephenolizing a liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling the formic acid from said 'mixture, under a pressure ranging from 15 to 40 millimetres mercury gauge, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

. 8. A process for dephenolizing a liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling from said mixture the greater part of the formic acid under reduced pressure, the remainder being distilled off at ordinary pressure, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

9. A process for dephenolizing a'liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from said liquid hydrocarbon, dividing said mixture into two parts, distilling under reduced pressure from each part separately the formic acid while combining the distillates, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

10. A process for dephenolizing a liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid, phenol thereby being dissolved in the formic.

acid, separating the mixture "of phenol and formic acid thus obtained from said liquid hydro carbon, dividing said mixture into twoparts, distilling under reduced pressure from each part separately the formic acid while combining the distillates, the distillation being initiated only with one of the said parts, the distillaion of the other part being started only after the concentration in formic acid of the distillate obtained from the first part begins to fall, so that the combined distillates have continuously a constant concentration in formic acid, and employing the distilled formic acid again for "dissolving phenol from a liquid hydrocarbon.

11. A process for dephenolizing a liquid hydrocarbon containing a phenol which comprises passing said liquid hydrocarbon in counter-current through formic acid, phenol thereby being dissolved in the formic acid, separating the mixture of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling the formic acid from said mixture, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

12. A process for dephenolizing a liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon with formic acid in several stages, phenol thereby being dissolved in the formic acid, separating the mixtures of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling the formic acid from said mixtures, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

13. A process for dephenolizing a liquid hydrocarbon containing a phenol, which comprises treating said liquid hydrocarbon in several stages with formic acid of successively increasing 6oncentrations, phenol thereby being dissolved in the formic acid, separating the mixtures of phenol and formic acid thus obtained from said liquid hydrocarbon, distilling the formic acid from said mixtures, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

14. A process for dephenolizing a tar oil containing pyridine and phenol, which comprises treating said tar oil with formic acid, separating the mixture of phenol, pyridine and formic acid thus obtained from said tar oil, distilling the formic acid from said mixture, and employing the distilled formic acid again for dissolving phenol from tar oil.

15. A process of dephenolizing a liquid hydrocarbon containing a phenol and a pyridine base, which comprises treating said liquid hydrocarbon with formic acid, the phenol and the pyridine base thereby being dissolved in the formic acid, separating the mixture of phenol, pyridine base and formic acid thus obtained from said liquid hydrocarbon, distilling the formic acid from said mixture, and employing the distilled formicacid again for dissolving phenol from a liquid hydrocarbon.

16. A process of dephenolizing a liquid hydrocarbon containing a phenol and a pyridine base, which comprises treating said liquid hydrocarbon with formic acid, the phenol and the pyridine base thereby being dissolved in the formic acid, separating the mixture of phenol, pyridine base and formic acid thus obtained from said liquid hydrocarbon, distilling under reduced pressure the formic acid from said mixture, and employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

17. A process of dephenolizing a liquid hydrocarbon containing a phenol and a pyridine base, which comprises treating said liquid hydrocarbon with formic acid, the phenol and the pyridine base thereby being, dissolved in the formic acid, separating the mixture of phenol, pyridine base and formic acid from said liquid hydrocarbon, distilling the formic acid from said mixture, under such reduced pressure that the distillation occurs below C., and'employing the distilled formic acid again for dissolving phenol from a liquid hydrocarbon.

HANS RODS. EMU.- SCHWA'MIBERGER. 

